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1 Department of Animal Science, University of Wyoming, Laramie, Wyoming, 82071-3684
* To whom correspondence should be addressed. E-mail: brethess{at}uwyo.edu.
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Abstract |
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Two experiments were conducted with lactating Angus x Gelbvieh beef cows to determine the effects of postpartum lipid supplementation, BCS at parturition, and day of lactation on fatty acid profiles in plasma, adipose tissue, and milk. In Exp. 1, 36 primiparous cows (488 ± 10 kg initial BW; 5.5 ± 0.02 initial BCS) were given ad libitum access to hay and assigned randomly to either a low-fat (control) supplement or supplements with either cracked high-linoleate safflower seeds (linoleate) or cracked high-oleate safflower seeds (oleate) from d 3 to 90 of lactation. Diets were formulated to be isonitrogenous and isocaloric; safflower seed diets provided 5% of DMI as fat. Plasma and milk samples were collected on d 30, 60, and 90 of lactation. Adipose tissue biopsies were collected near the tail-head region of cows on d 45 and 90 of lactation. In Exp. 2, 3-yr-old cows managed to achieve a BCS of 4 ± 0.07 (479 ±36 kg of BW) or 6 ± 0.07 (580 ± 53 kg of BW) at parturition were used in a 2-yr experiment (n = 36/yr). Beginning 3 d postpartum, cows were fed diets similar to Exp. 1 through d 61 of lactation. Adipose tissue and milk samples were collected on d 30 and 60, and plasma was collected on d 31 and 61 of lactation. Responses to postpartum dietary treatment were comparable in both experiments. Cows fed linoleate and oleate had greater (P < 0.001) total fatty acid concentrations in plasma than cows fed control. Except for 15:1, milk fatty acids with <18 carbons were greatest (P 
0.01) for cows fed control, whereas milk from cows fed linoleate had the greatest (P 0.02) 18:1trans-11, 18:2n-6, and cis-9, trans-11 CLA. Milk from cows fed oleate had the greatest (P < 0.001) 18:1cis-9. In Exp. 1, total fatty acid concentrations in adipose tissue samples decreased at d 90 compared with d 45 of lactation, but fatty acid profile of cow adipose tissue was not affected (P = 0.14 to 0.80) by dietary treatment. In Exp. 2, percentage of cis-9, trans-11 CLA in adipose tissue of cows in BCS of 6 decreased (P = 0.001) from d 30 to 60 of lactation. Plasma and milk fatty acid composition reflected alterations in postpartum diet. Less medium-chain fatty acids and more 18-carbon fatty acids in milk were indicative of reduced de novo fatty acid synthesis in the mammary gland of beef cows fed lipid supplements; however, metabolic demands of lactation prevented the deposition of exogenously derived fatty acids in adipose tissue through d 90 of lactation.
Key Words: adipose tissue, beef cows, body condition score, fatty acids, lipid supplementation, milk
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